MONDAY, Feb. 28 (HealthDay News) -- Many American women abandoned hormone replacement therapy after a 2002 study found the treatment was tied to higher breast cancer risk. A sharp drop in breast cancer incidence among whites was observed soon after.

However, a new study suggests that the 2002-2003 decline in breast cancer incidence among white women did not continue through 2007.

The data suggests that the drop in breast cancers linked to women abandoning hormone replacement therapy (HRT) has now bottomed out.

Breast cancer rates among U.S. white women fell by about 7 percent between 2002 and 2003 after the release in 2002 of findings from the Women's Health Initiative study that linked HRT with an increased risk of breast cancer.

To examine whether that trend has continued, American Cancer Society and U.S. National Cancer Institute (NCI) researchers reviewed breast cancer data collected from 2000 to 2007 by NCI Surveillance, Epidemiology and End Results (SEER) registries across the country.

The analysis revealed that the sharp decline in breast cancer rates among white women that occurred between 2002 and 2003 did not continue between 2003 and 2007. Instead, breast cancer rates among white women remained relatively stable from 2003 to 2007.

"Postmenopausal hormone replacement therapy certainly had accounted for an increase in the incidence of developing a breast cancer. The use of postmenopausal HRT had sharply declined after multiple reports proved this relationship," noted one expert, Dr. Sharon M. Rosenbaum-Smith, a breast cancer specialist and surgeon at the Comprehensive Breast Center at St. Luke's-Roosevelt Medical Center in New York City.

"As more women stop using HRT, and less women start it after reaching menopause, it would be expected that the incidence [of breast cancer] would plateau at some point," she said. "This study is promising in that it has not shown an increase in the incidence of breast cancer, and the stopping of HRT use can certainly be a contributing factor to this plateau."

The new report notes, however, that the 2002-2003 trend only showed up among white women: there was no major decrease in breast cancer rates among black and Hispanic women between 2002 and 2003, and no significant changes in breast cancer rates for those groups of women from 2003 to 2007.

According to the ACS/NCI study authors, there are a number of possible factors that could explain the leveling out of breast cancer rates among white women in recent years:

• The decrease in HRT use after 2003 may not have been large enough to continue delaying breast cancer diagnoses.
• The trends may reflect improved sensitivity of mammography without the influence of HRT, since HRT increases breast density and compromises the diagnostic performance of mammograms and breast biopsies.
• Breast cancer rates may reflect the relatively stable rates of screening mammography in the United States since 2000. An increase in screening rates would have likely been associated with an increased number of breast cancer diagnoses.

The study was released online in advance of publication in a future print issue of the journal Cancer Epidemiology, Biomarkers & Prevention.

More information

The U.S. National Cancer Institute has more about menopausal hormone replacement therapy and cancer.